reorder docs (pct after qm)

[pve-docs.git] / pvecm.adoc

diff --git a/pvecm.adoc b/pvecm.adoc
index 1a3a7e8f51b23890e3fadf0b8f0777faa596b34e..e6e2058d73ed813d272d2a91dbe692eb6b51a2ec 100644 (file)
--- a/pvecm.adoc
+++ b/pvecm.adoc
@@ -59,7 +59,7 @@ Requirements
 * All nodes must be in the same network as corosync uses IP Multicast
  to communicate between nodes (also see
  http://www.corosync.org[Corosync Cluster Engine]). Corosync uses UDP
 * All nodes must be in the same network as corosync uses IP Multicast
  to communicate between nodes (also see
  http://www.corosync.org[Corosync Cluster Engine]). Corosync uses UDP

- ports 5404and 5405 for cluster communication.
+ ports 5404 and 5405 for cluster communication.

 +
 NOTE: Some switches do not support IP multicast by default and must be
 manually enabled first.
 +
 NOTE: Some switches do not support IP multicast by default and must be
 manually enabled first.


@@ -89,7 +89,6 @@ hostname and IP is not possible after cluster creation.
 Currently the cluster creation has to be done on the console, so you
 need to login via 'ssh'.
 
 Currently the cluster creation has to be done on the console, so you
 need to login via 'ssh'.
 

-

 Create the Cluster
 ------------------
 
 Create the Cluster
 ------------------
 


@@ -98,6 +97,10 @@ your cluster. This name cannot be changed later.
 
  hp1# pvecm create YOUR-CLUSTER-NAME
 
 
  hp1# pvecm create YOUR-CLUSTER-NAME
 

+CAUTION: The cluster name is used to compute the default multicast
+address. Please use unique cluster names if you run more than one
+cluster inside your network.
+

 To check the state of your cluster use:
 
  hp1# pvecm status
 To check the state of your cluster use:
 
  hp1# pvecm status


@@ -278,6 +281,45 @@ cluster again, you have to
 * then join it, as explained in the previous section.
 
 
 * then join it, as explained in the previous section.
 
 

+Quorum
+------
+
+{pve} use a quorum-based technique to provide a consistent state among
+all cluster nodes.
+
+[quote, from Wikipedia, Quorum (distributed computing)]
+____
+A quorum is the minimum number of votes that a distributed transaction
+has to obtain in order to be allowed to perform an operation in a
+distributed system.
+____
+
+In case of network partitioning, state changes requires that a
+majority of nodes are online. The cluster switches to read-only mode
+if it loose quorum.
+
+NOTE: {pve} assigns a single vote to each node by default.
+
+
+Cluster Cold Start
+------------------
+
+It is obvious that a cluster is not quorate when all nodes are
+offline. This is a common case after a power failure.
+
+NOTE: It is always a good idea to use an uninterruptible power supply
+('UPS', also called 'battery backup') to avoid this state. Especially if
+you want HA.
+
+On node startup, service 'pve-manager' is started and waits for
+quorum. Once quorate, it starts all guests which have the 'onboot'
+flag set.
+
+When you turn on nodes, or when power comes back after power failure,
+it is likely that some nodes boots faster than others. Please keep in
+mind that guest startup is delayed until you reach quorum.
+
+

 ifdef::manvolnum[]
 include::pve-copyright.adoc[]
 endif::manvolnum[]
 ifdef::manvolnum[]
 include::pve-copyright.adoc[]
 endif::manvolnum[]